A universal hippocampal memory code across animals and environments

How learning generalizes across contexts is a fundamental question in neuroscience, as successful behavior often requires transferring acquired knowledge to new environments. Conditioning tasks provide a clear example of such generalization, with learned responses rapidly expressed across distinct spatial contexts. A central challenge in understanding the neural basis of this ability is determining how the hippocampus represents task-related information across environments, given that its spatial representations remap with context. Here, we used calcium imaging to record hippocampal population activity as rats performed a conditioning task across multiple spatial contexts. To characterize task-related population structure, we applied dimensionality reduction and alignment methods to construct low-dimensional manifolds of hippocampal activity. We found that task-related population activity occupied a stable geometric structure across contexts, despite pronounced remapping of spatial representations. Strikingly, this task-related geometry was conserved not only across contexts within individual animals but also across animals, revealing a shared organization of task representations in the hippocampus. These findings provide a population-level account of how task-related information is preserved across changing spatial environments and suggest that hippocampal task representations follow shared population-level geometric organization across individuals.